The present invention relates to rocket engine nozzles having movable diverging sections. The field of application of the invention is more particularly but not exclusively that of missiles.
A nozzle with a movable diverging section generally makes use of a ball joint or sphere/sphere type connection between the stationary throat and the movable diverging section of the nozzle. The technology making use of a movable diverging section for steering thrust presents numerous advantages, for given bulk, compared with other known technologies for steering thrust such as those making use of a steerable nozzle on a flexible abutment, for example. Nozzles in which only the diverging section is movable present capacities for thrust deflection that are considerably greater than those that can be obtained with steerable nozzles in which the entire passage of the nozzle is movable. This improvement in thrust deflection can be explained by the presence, in the movable zone of the diverging section and in the tilted configuration, of an asymmetrical pressure field that leads to a gain that is greater than 1 compared with the geometrical effect on its own. This technology and its advantages compared with other types of steerable nozzle are described in particular in Document U.S. Pat. No. 6,948,307.
Nevertheless, in this type of nozzle, the throat and the portion of the diverging section that is in sliding contact with the throat can be subjected to high levels of thermal-erosion phenomena. Under certain conditions of tilting the diverging section, the combustion gas can present not only a temperature that is very high, but also a circumferential speed that is very high (potentially sonic). In order to withstand these thermal-erosion effects, parts constituting the ball joint connection are made of thermostructural composite materials, which are known for their good mechanical properties and for their ability to conserve those properties at high temperature. In particular, they comprise carbon/carbon (C/C) composites made of carbon fiber reinforcement densified with a carbon matrix.
Thermostructural composite materials are high performance materials and consequently they have a high manufacturing cost.
In addition, when using parts made of C/C composite material for the ball joint connection, the coefficient of friction between those parts increases with increasing temperature, thereby requiring higher activation power in order to tilt the diverging section while it is in operation.
There thus exists a need to have a solution enabling a nozzle with a movable diverging section to be made at lower manufacturing costs and requiring lower activation energy.